Sheet processing apparatus

ABSTRACT

A sheet processing apparatus according to this invention is for sorting and discharging papers supplied from an image forming apparatus, and includes an alignment device configured to shift the papers transported from the image forming apparatus into a direction orthogonal to the direction of the transport and thus align the papers in the direction of width, and a paper discharge unit configured to guide the aligned and shifted papers to a discharge port and discharge the shifted papers from the discharge port and at different angles from each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a sheet processing apparatus that performs post-processing of sheets discharged from an image forming apparatus such as a copy machine, printer, or multifunction peripheral.

2. Description of the Related Art

Recently, for some image forming apparatuses, a sheet post-processing apparatus is provided next to the paper discharge unit in the body of the image forming apparatus in order to perform post-processing such as sorting sheets after images are formed thereon, or performing stapling processing to the sheets.

JP-A-5-139610 (laid open on Jun. 8, 1993) describes a sheet post-processing apparatus that can carry out sorting processing of sheets. In this example, it is described that an aligning unit that aligns a sheet pack is provided and the alignment position of the sheet pack is shifted, thereby discharging each sheet of the sheet pack in an offsetting manner.

Also, JP-A-5-278921 (laid open on Oct. 26, 1993) describes a paper discharge tray mounted on an image forming apparatus. The paper discharge tray in this example can freely open and close in a sectorial form.

Moreover, JP-A-2001-2314 (laid open on Jan. 9, 2001) describes a sheet processing apparatus that sorts sheets into plural tray groups. In this example, the plural tray groups attached to an image forming apparatus can be turned in a sectorial form.

However, in the above examples, no technique is described for clarifying the distribution of sheets when sorting the sheets.

This invention provides a sheet processing apparatus that enables discharge of sheets in a distributed manner to a predetermined angular direction when performing sorting processing of the sheets.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration view showing a sheet processing apparatus according to an embodiment of this invention.

FIG. 2 is a perspective view showing essential parts of the sheet processing apparatus of this invention.

FIG. 3 is an explanatory view showing a paddle of the sheet processing apparatus of this invention.

FIG. 4 is a schematic perspective view showing a longitudinal alignment roller of the sheet processing apparatus of this invention.

FIG. 5 is a schematic perspective view showing a standby tray and a processing tray of the sheet processing apparatus of this invention.

FIG. 6 is a top view showing the standby tray and the processing tray of the sheet processing apparatus of this invention.

FIG. 7 is a schematic perspective view showing a lateral alignment plate and a transport belt of the sheet processing apparatus of this invention.

FIG. 8 is a block diagram showing a control system of the sheet processing apparatus of this invention.

FIG. 9 is an explanatory view showing an operation of sorting processing in the sheet processing apparatus of this invention.

FIG. 10 is an explanatory view showing another operation of sorting processing in the sheet processing apparatus of this invention.

FIG. 11 is an explanatory view showing still another operation of sorting processing in the sheet processing apparatus of this invention.

FIG. 12 is an explanatory view showing an operation of a sheet discharge unit in the sheet processing apparatus of this invention.

FIG. 13 is an explanatory view showing another operation of the sheet discharge unit in the sheet processing apparatus of this invention.

DETAILED DESCRIPTION OF THE INVENTION

Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus of the present invention.

Hereinafter, an embodiment of this invention will be described in detail with reference to the drawings. In the drawings, the same parts are described with the same reference numerals.

FIG. 1 is a schematic configuration view showing a sheet post-processing apparatus 2 with an image forming apparatus 1 such as a copy machine arranged next to it. A paper P on which an image has been formed by the image forming apparatus 1 is discharged from paper discharge rollers 4 and transported to the sheet post-processing apparatus 2. The paper discharge rollers 4 include an upper roller 4 a and a lower roller 4 b.

The sheet post-processing apparatus 2 has a standby tray 10, a processing tray 12, a stapler 14, a first paper discharge tray 16, a second paper discharge tray 18, and a fixed tray 20.

The paper P discharged by the paper discharge rollers 4 of the image forming apparatus 1 is received by entry rollers 22 provided near an entry port of the sheet post-processing apparatus 2. The entry rollers 22 include an upper roller 22 a and a lower roller 22 b and are driven by a motor (not shown).

Paper feed rollers 24 are provided downstream of the entry rollers 22. The paper P received by the entry rollers 22 is sent to the standby tray 10 via the paper feed rollers 24. Between the entry rollers 22 and the standby tray 10, a paper path 23 for guiding the paper P to the paper feed rollers 24 is provided. The paper feed rollers 24 include an upper roller 24 a and a lower roller 24 b.

The standby tray 10 has the papers P stacked thereon and is structured to be openable. When a predetermined number of papers P are stacked thereon, the standby tray 10 opens and the papers P fall down to the processing tray 12 because of their own weight. Below the standby tray 10, the processing tray 12 is provided on which the papers P falling from the standby tray 10 are stacked. The processing tray 12 aligns and supports the papers P while the stapler 14 as a post-processing mechanism staples the papers P.

The papers that have fallen onto the processing tray 12 are guided to the stapler 14 by rollers 28 and stapling processing is performed. The rollers 28 include an upper roller 28 and a lower roller 28 b. In the case of performing stapling processing, the plural papers P that have fallen onto the processing tray 12 from the standby tray 10 are aligned in the longitudinal direction, which is the transporting direction, and also aligned in the lateral direction orthogonal to the transporting direction, and are then stapled.

Turnable paddles 40 are arranged at a position to which the rear end of the papers P falls when the papers P fall onto the processing tray 12.

The paddles 40 are attached to a rotary shaft 26 and are to slap down the papers P falling from the standby tray 10 onto the processing tray 12 and thus send the papers P toward the stapler 14. The details of the paddles 40 will be later described with reference to FIG. 3.

A stopper 45 that regulating the rear end position of the papers P is provided at the end of the processing tray 12 near the stapler 14. Also, a transport belt 50 is provided that transports the sorted or stapled papers P to the first paper discharge tray 16 or the second paper discharge tray 18.

The transport belt 50 is laid between pulleys 36 and 38. The transport belt 50 has a pawl member 50 a attached thereto that hooks the rear end of the papers P and sends them. The lower roller 28 b of the rollers 28 is arranged coaxially with the pulley 38. The rollers 28 rotate in opposite directions when guiding the aligned papers toward the stapler 14 and when discharging the stapled papers P.

The pulley 36 is attached to a shaft 34, and plural discharge rollers 30 are rotatably attached to this shaft 34. The discharge rollers 30 will be described with reference to FIG. 2.

The papers P transported by the transport belt 50 are discharged to the first paper discharge tray 16 or the second paper discharge tray 18, and the first paper discharge tray 16 and the second paper discharge tray 18 are lifted and lowered by a driving unit (not shown) and thus receive the papers P.

Also, the papers P stacked on the standby tray 10 may be discharged to the first paper discharge tray 16 or the second paper discharge tray 18 without being stapled. In this case, the papers P are discharged by a roller 32 without causing them to fall onto the processing tray 12.

The standby tray 10 is arranged at an inclination angle of θ1 to support the papers P in the state where the distal end of the papers P is higher than their rear end. Also the paper discharge trays 16 and 18 are arranged at an inclination angle θ2 to support the papers P in the state where the distal end of the papers P is higher than their rear end.

The papers P that do not require post-processing can also be discharged to the fixed tray 20. A transport passage to guide the papers P to the fixed tray 20 is provided, though not shown.

FIG. 2 is a perspective view of essential parts of the sheet post-processing apparatus 2, as viewed from the direction of the arrow x in FIG. 1.

In FIG. 2, the shaft 34 is arranged orthogonally to the direction of transporting the papers P. The pulley 36 is attached to an intermediate part of the shaft 34 and the belt 50 is laid on this pulley 36. The discharge rollers 30 include central rollers 30 a, 30 a and side rollers 30 b, 30 c. The central rollers 30 a are attached to both sides of the pulley 36, and the turning of the belt 50 causes the central rollers 30 a to rotate, too.

The side rollers 30 b and 30 c are attached to two side parts of the shaft 34. The side rollers 30 b and 30 c are symmetrically arranged about the central rollers 30 a.

The central rollers 30 a rotate, interlocked with the driving of the belt 50. The side roller 30 b and the side roller 30 c are rotationally controlled by their respective driving units synchronously with the rotation of the central rollers 30 a, and they rotate when discharging the papers P to the tray 16 or 18.

FIG. 3 shows the configuration of the paddle 40. The paddle 40 has its attachment member 41 attached to the rotary shaft 26. The attachment member 41 includes a receiving part 42 that receives the rear end of the papers P falling from the standby tray 10, a slapping part 43 that slaps the papers P down onto the processing tray 12, and a feed part 44 that feeds the papers P on the processing tray 12 toward the stapler 14.

In the case of feeding the papers P on the processing tray 12 toward the stapler 14 (arrow q), the upper roller 28 a of the rollers 28 rotates counterclockwise and the lower roller 28 b rotates clockwise. In the case of discharging the papers P on the processing tray 12, the upper roller 28 a rotates in the direction of the arrow r and the lower roller 28 b rotates in the direction of the arrow s.

The rotary shaft 26 is rotationally driven by a motor 54 (see FIG. 4). Alternatively, the rotation force of the motor can be transmitted to the rotary shaft 26 via a gear mechanism. The slapping part 43 and the feed part 44 of the paddle 40 are made of a rubber material and are elastic.

As can be seen from FIG. 2, the plural paddles 40 are attached to the rotary shaft 26. Moreover, guide members 52 are provided to guide the papers to the processing tray 12. The guide members 52 serve as guides when pulling the rear end of the transported papers P toward the stapler 14.

FIG. 4 is a schematic perspective view showing the configuration of the rollers 28 for longitudinal alignment of the papers P and the transport belt 50. As shown in FIG. 4, the transport belt 50 is laid between the pulleys 36 and 38 and is rotationally driven by a motor 56, thus moving in a circulating manner between the stapler 14 and a paper discharge port 100 (FIG. 1) along the direction of discharging the papers.

When transporting the papers P toward the paper discharge trays 16 and 18, the transport belt 50 moves in the direction of the arrow t and the upper roller 28 a and the lower roller 28 b for longitudinal alignment rotate in the direction of the arrow r and the direction of the arrow s shown in FIG. 3. The upper roller 28 a for longitudinal alignment is rotationally driven by a motor 58. The lower roller 28 b is rotationally driven by the motor 56, which drives the transport belt 50.

FIG. 5 and FIG. 6 schematically show the standby tray 10 and the processing tray 12. The standby tray 10 has a pair of tray members 10 a, 10 b. They receive the papers P in the state of being slid to the width of the papers P and support both sides of the papers P. On the tray members 10 a, 10 b, standby stoppers 10 c, 10 d to regulate the rear end of the papers P are provided.

The standby tray 10 is slid in the directions of the arrows m and n by a motor (not shown). Before the papers P reach the processing tray 12 from the standby tray 10, the papers P may deviate in the lateral direction orthogonal to the transporting direction when the papers P on the standby tray 10 are dropped and supplied to the processing tray 12.

Therefore, a lateral alignment device 46 that prevents the deviation of the papers P is provided, as shown in FIG. 7. The lateral alignment device 46 has a pair of lateral alignment plates 47 a, 47 b. The lateral alignment plates 47 a, 47 b are slidable in the direction v to fit the width of the papers P, and the alignment position can be changed by a motor 48.

Also, the lateral alignment device 46 is used for sorting and discharging papers by controlling the movement of the lateral alignment plates 47 a, 47 b.

The driving units such as the motors 48, 54, 56 and 58 that drive the above various mechanisms are drive-controlled by a control circuit.

Next, a post-processing operation by the sheet post-processing apparatus 2 will be described along the flow of papers. The post-processed papers are discharged to either the paper discharge tray 16 or the paper discharge tray 18. Hereinafter, the case of discharging the papers to the paper discharge tray 16 will be described as a representative example.

The papers P transported from the entry rollers 22 via the paper path ceiling 23 are supplied onto the standby tray 10 by the paper feed rollers 24. Next, the papers P fall onto the processing tray 12.

When the papers P fall, the upper roller 28 a for longitudinal alignment is retreating above and the receiving parts 42 of the paddles 40 receive the rear end of the papers P.

Then, the paddles 40 rotate in the direction of the arrow y as shown in FIG. 3. The rear end of the papers P falls off the receiving parts 42, and the slapping parts 43 slap the papers down to the processing tray 12. The papers fall while both lateral sides of the papers P contact the lateral alignment plates 47 a, 47 b, thus performing lateral alignment. Moreover, the paddles 40 send the papers P in the direction of the arrow q by the feed parts 44. As the rear end of the papers P is abutted against the stopper 45, longitudinal alignment of the papers P is completed.

In this way, the papers P on which images have been formed are guided from the paper feed rollers 24 to the processing tray 12 while the papers are sequentially aligned laterally and longitudinally.

In the case of performing stapling processing, when the number of papers P stacked on the processing tray 12 has reached a predetermined number, the stapler 14 staples the papers P on the processing tray 12 at a desired position and thus forms a sheet pack. After this, the upper roller 28 a rotating in the direction of the arrow r and the lower roller 28 b rotating in the direction of the arrow s, as shown in FIG. 3, nip and transport the sheet pack toward the paper discharge tray 16.

When the rear end of the sheet pack has passed the rollers 28 a, 28 b, it is hooked by the feed pawl 50 a of the transport belt 50, transported toward the paper discharge tray 16, and then discharged onto the paper discharge tray 16 by the discharge rollers 30.

Meanwhile, in the case of performing sorting processing as post-processing, the lateral position of the papers P is shifted one by one by the lateral alignment plates 47 a, 47 b and the papers are thus discharged onto the paper discharge tray 16.

The overall operations of the sheet post-processing apparatus 2 have been described above. Next, the configuration of a sorting processing unit, which is a characteristic unit of this invention, will be described.

FIG. 8 is a block diagram showing a control system that controls the sorting processing unit. In FIG. 8, 60 denotes a control circuit that controls the image forming apparatus 1. It is formed by, for example, a microprocessor including a CPU and controls an image forming unit 64 or the like in response to an operation of an operating unit 62. The operating unit 62 has keys for entering the number of print sheets and the like, and an instruction unit 66 that instructs post-processing such as sorting processing.

Numeral 70 denotes a control circuit that controls the sheet post-processing apparatus 2. It is formed by, for example, a microprocessor including a CPU, transmits information to and from the control circuit 60 for the image forming apparatus 1, and controls each part for sheet post-processing so that the image forming operation and the operation of the sheet post-processing apparatus 2 are linked with each other.

Also, the control circuit 70 is connected to a paper discharge control unit 72 that controls the rotation of the discharge rollers 30 a, 30 b, 30 c, and to a sorting control unit 80 that controls the lateral alignment plates 47 a, 47 b to sort the papers P.

The paper discharge control unit 72 has a first driver 74 that controls the turning or rotation of the transport belt 50 and the discharge rollers 30 a, a second driver 76 that controls the rotation of the discharge roller 30 b, and a third driver 78 that controls the rotation of the discharge roller 30 c.

The discharge rollers 30 a, 30 b, 30 c are controlled by the first driver 74, the second driver 76 and the third driver 78. When discharging normal papers P, the discharge rollers 30 a, 30 b, 30 c rotate at the same speed synchronously with each other. However, when discharging sorted papers P, the discharge rollers take different rotation forms from each other.

Also, the sorting control unit 80 controls the motor 48 (FIG. 7) to slide the positions of the lateral alignment plates 47 a, 47 b.

FIG. 9 and FIG. 10 are explanatory views for explaining the operations of the paper discharge unit under the control of the control circuits 60 and 70.

In the case of sorting and discharging the papers P, for example, in the case of making two copies of plural originals, then sorting and discharging them, the papers P are shifted one by one alternately in the direction of width by the lateral alignment plates 47 a, 47 b and thus discharged to the paper discharge tray 16.

FIG. 9 shows a discharge state in ordinary sorting processing. It shows an example in which the first paper P1 and the second paper P2 are shifted in the direction of width and thus discharged. The first paper P1 is shifted to the left in FIG. 9 by the lateral alignment plates 47 a, 47 b (indicated by the solid line). The second paper P2 is shifted to the right in FIG. 9 by the lateral alignment plates 47 a, 47 b (indicated by the dotted line) These papers are thus discharged to the paper discharge tray 16 by the rotation of the discharge rollers 30 a, 30 b, 30 c.

The third paper is discharged to the same position as the first paper P1, and the fourth paper is discharged to the same position as the second paper P2. The subsequent papers are similarly discharged to the alternately shifted positions. Alternately moving the lateral alignment plates 47 a, 47 b to shift the papers P1, P2 is carried out by the sorting control unit 80.

FIG. 10 is for explaining another operation of sorting processing according to this invention. FIG. 10 is similar to FIG. 9 in that the first paper P1 is shifted to the left in FIG. 10 by the lateral alignment plates 47 a, 47 b (indicated by the solid line) and the second paper P2 is shifted to the right in FIG. 10 by the lateral alignment plates 47 a, 47 b (indicated by the dotted line).

Also, the papers P1, P2 are discharged to the paper discharge tray 16 by the rotation of the discharge rollers 30 a, 30 b, 30 c, but the rotating states of the discharge rollers 30 b, 30 c change before the papers are discharged to the paper discharge tray 16.

That is, while the first paper P1 is discharged toward the paper discharge tray 16, the rotation speed of the discharge roller 30 b becomes lower than the rotation speed of the discharge rollers 30 a, and the rotation speed of the discharge roller 30 c becomes higher than the rotation speed of the discharge rollers 30 a. Thus, the discharge of the paper P1 at the left end in the direction of width becomes slower and the discharge at the right end becomes faster. Therefore, the paper P1, shifted to the left in FIG. 10, is further inclined to the left and discharged.

On the other hand, when discharging the second paper P2, while the second paper P2 is discharged toward the paper discharge tray 16, the rotation speed of the discharge roller 30 b becomes higher than the rotation speed of the discharge rollers 30 a, and the rotation speed of the discharge roller 30 c becomes lower than the rotation speed of the discharge rollers 30 a. Thus, the discharge of the paper P2 at the left end in the direction of width becomes faster and the discharge at the right end becomes slower. Therefore, the paper P2, shifted to the right in FIG. 10, is further inclined to the right and discharged.

As a result, the papers P1 and P2 are discharged to the paper discharge tray 16 as they are inclined at a predetermined angle into diffusing directions from each other. Similarly, the subsequent papers are sequentially inclined at a predetermined angle alternately in diffusing directions from each other and are discharged to the paper discharge tray 16.

The first, second and third drivers 74, 76, 78 control the rotation speeds of the discharge rollers 30 a, 30 b, 30 c, and when discharging the papers P1, P2, these rollers rotate at the same rotation speed up to a certain point. Also, while the papers P1, P2 are discharged, the rotation speeds of the discharge rollers 30 b and 30 c are relatively switched without changing the rotation speed of the discharge rollers 30 a, thus inclining the papers P1, P2.

Moreover, the rotation of the discharge rollers 30 a, 30 b, 30 c is stopped immediately before the papers P1, P2 are discharged to the paper discharge tray 16. Thus, the papers P1, P2 are discharged to the paper discharge tray 16 by inertia.

As the rotation speed of the discharge rollers 30 a is thus kept constant and the rotation speeds of the discharge roller 30 b and the discharge roller 30 c are alternately made higher or lower, the papers can be inclined to different directions from each other and discharged.

Also, since corners P01, P02 of the papers P1, P2 protrude from the paper discharge tray 16, as shown in FIG. 10, one can take out the papers P1, P2 by holding these corners P01, P02, and the take-out after the sorting processing can be easier.

The directions of discharging the papers P1, P2 and the like may be the opposite directions to those shown in FIG. 10. That is, when the discharge of the left end of the paper P1 in the direction of width is made faster and the discharge of the right end is made slower, the paper P1 is inclined to the right and discharged, as shown in FIG. 11. On the other hand, when the discharge of the left end of the paper P2 in the direction of width is made slower and the discharge of the right end is made faster, the paper P2 is inclined to the left in FIG. 11 and discharged. Thus, the shifted papers P1, P2 can be discharged into angular directions that cross each other.

Also in this case, since corners P01, P02 of the papers P1, P2 protrude from the paper discharge tray 16, as shown in FIG. 11, one can take out the papers P1, P2 by holding these corners P01, P02, and the take-out after the sorting processing can be easier.

Also, since the paper discharge tray 16 is inclined at the inclination angle 02 as described with reference to FIG. 1, the discharged papers P1, P2 and the like slip and fall in this state. The inclinations of the discharged papers may be lost, and this may cause the state of FIG. 9.

Thus, a movable pin 90 is provided on the paper stacking surface of the paper discharge tray 16, and in the case of performing sorting processing, the pin 90 can be protruded from the paper discharge tray 16. Thus, even when the papers P1, P2 discharged at predetermined angles are about to slip down because of the inclination angle θ2 of the tray 16, it can be prevented by the pin 90.

When the pin 90 is protruded, the thickness of the papers stacked on the paper discharge tray 16 may exceed the height of the pin 90 in some cases. Therefore, the pin 90 may be configured to movably protrude from the body of the sheet post-processing apparatus 1.

FIG. 12 shows the case where the pin 90 is protruded on the paper stacking surface of the paper discharge tray 16. FIG. 13 shows the case where a pin 91 is protruded from the body of the sheet post-processing apparatus 1.

Also, FIG. 12 is a view for explaining the state before the papers P are discharged to the paper discharge tray 16, and FIG. 13 is a view for explaining the state after the papers P are discharged to the paper discharge tray 16.

Moreover, the angle of the paper discharge tray 16 can be made adjustable, instead of providing the pin 90 or 91. In this case, when performing sorting processing and discharging papers, the inclination angle θ2 can be decreased so that the paper stacking surface becomes closer to a flat surface.

In this manner, according to this invention, a sheet post-processing apparatus can be provided in which, when discharging papers to the paper discharge tray, the papers are distributed into different angular directions and thus discharged, thus clarifying the distinction of the sorted papers.

This invention is not limited to the above description and various modifications can be made without departing form the claims. For example, stapled sheet packs can be sorted and discharged. Also, the paper discharge control unit 72 may be controlled in accordance with the mode selection by the user so that a mode of discharging without inclination as shown in FIG. 9 and a mode of discharging with inclination as shown in FIG. 10 or FIG. 11 can be selected.

Although exemplary embodiments of the present invention have been shown and described, it will be apparent to those having ordinary skills in the art that a number of changes, modifications, or alterations to the invention as described herein may be made, none of which depart from the spirit of the present invention. All such changes, modifications, and alterations should therefore be seen as within the scope of the present invention. 

1. A sheet processing apparatus capable of sorting and discharging papers supplied from an image forming apparatus, comprising: an alignment device configured to shift the papers sequentially transported from the image forming apparatus into a first direction orthogonal to the direction of the transport and a second direction opposite to the first direction, and thus align the papers in the direction of width; a paper discharge unit configured to guide the papers aligned by the alignment device to a discharge port and discharge the papers shifted to the first direction and the second direction, from the discharge port and at different angles from each other; and a paper discharge tray configured to receive the papers discharged from the discharge port.
 2. The sheet processing apparatus according to claim 1, wherein the paper discharge unit discharges the papers shifted to the first direction and the second direction, into angular directions dispersing from each other.
 3. The sheet processing apparatus according to claim 1, wherein the paper discharge unit discharges the papers shifted to the first direction and the second direction, into angular directions crossing each other.
 4. The sheet processing apparatus according to claim 1, wherein the paper discharge unit has a first roller member that guides the papers aligned by the alignment device to the discharge port, and plural discharge rollers arranged on a shaft orthogonal to the direction of discharge of the papers, the plural discharge rollers including a first discharge roller that supports a central part of the papers to be discharged and second and third discharge rollers that support both side of the papers to be discharged, and the papers guided by the first roller member are transported to the discharge port by rotations of the first, second and third discharge rollers, and in the course of the transport, the rotation speeds of the second and third discharge rollers are relatively switched with reference to the rotation speed of the first discharge roller.
 5. The sheet processing apparatus according to claim 4, wherein the paper discharge unit alternately switches the rotation speeds of the second and third discharge rollers every time the paper shifted to the first direction and the paper shifted to the second direction are discharged.
 6. The sheet processing apparatus according to claim 4, wherein the paper discharge unit stops the rotation of the first, second and third discharge rollers immediately before the papers shifted to the first direction and the second direction are discharged to the paper discharge tray.
 7. The sheet processing apparatus according to claim 1, wherein the paper discharge tray is arranged at a predetermined inclination angle, and is provided with a slip preventing member for reducing slip of the papers discharged at a predetermined angle to the paper discharge tray because of the inclination angle.
 8. The sheet processing apparatus according to claim 7, wherein the slip preventing member includes a pin that can protrude on a paper stacking surface of the paper discharge tray when sorting and discharging the papers.
 9. The sheet processing apparatus according to claim 7, wherein the slip preventing member includes a pin that can protrude from the discharge port side to a paper stacking surface of the paper discharge tray when sorting and discharging the papers.
 10. The sheet processing apparatus according to claim 1, wherein the paper discharge tray has an angular-adjustable paper stacking surface, and the paper stacking surface becomes closer to a flat surface when sorting and discharging the papers.
 11. The sheet processing apparatus according to claim 1, wherein the alignment devices includes a pair of lateral alignment plates that align the papers in the direction of width, and alternately shifts the papers sequentially transported from the image forming apparatus into the first direction and the second direction by moving the pair of lateral alignment plates.
 12. A sheet processing apparatus capable of sorting and discharging papers supplied from an image forming apparatus, comprising: an alignment device including a pair of alignment plates that align the papers in the direction of width, and capable of shifting the papers sequentially transported from the image forming apparatus into a first direction orthogonal to the direction of the transport and a second direction opposite to the first direction; a paper discharge unit including a first discharge roller that is arranged near a paper discharge port and that supports a central part of the papers to be discharged, and second and third discharge rollers that support both sides of the papers to be discharged; a paper discharge tray configured to receive the papers discharged from the discharge port; a first control unit configured to shift the pair of alignment plates to the first direction and the second direction; and a second control unit configured to control rotation states of the first, second and third discharge rollers, transport the shifted papers to the discharge port, relatively switch the rotation speeds of the second and third discharge rollers with reference to the rotation speed of the first discharge roller, and thus control discharge angle of the papers.
 13. The sheet processing apparatus according to claim 12, wherein the second control unit rotates the first, second and third discharge rollers to transport the papers shifted to the first direction and the second direction, to the discharge port, and relatively switches the rotation speeds of the second and third discharge rollers in the course of the transport, thus controlling the discharge angle of the papers.
 14. The sheet processing apparatus according to claim 12, wherein the paper discharge unit alternately switches the rotation speeds of the second and third discharge rollers every time the paper shifted to the first direction and the paper shifted to the second direction are discharged.
 15. The sheet processing apparatus according to claim 12, wherein the paper discharge unit stops the rotation of the first, second and third discharge rollers immediately before the papers shifted to the first direction and second direction are discharged to the paper discharge tray. 